1. Field of the Invention
The present invention relates generally to audio processing, and more particularly to processing an audio signal to suppress noise.
2. Description of Related Art
Currently, there are many methods for reducing background noise in an adverse audio environment. A stationary noise suppression system suppresses stationary noise, by either a fixed or varying number of dB. A fixed suppression system suppresses stationary or non-stationary noise by a fixed number of dB. The shortcoming of the stationary noise suppressor is that non-stationary noise will not be suppressed, whereas the shortcoming of the fixed suppression system is that it must suppress noise by a conservative level in order to avoid speech distortion at low signal-to-noise ratios (SNR).
Another form of noise suppression is dynamic noise suppression. A common type of dynamic noise suppression systems is based on SNR. The SNR may be used to determine a degree of suppression. Unfortunately, SNR by itself is not a very good predictor of speech distortion due to the presence of different noise types in the audio environment. SNR is a ratio indicating how much louder speech is then noise. However, speech may be a non-stationary signal which may constantly change and contain pauses. Typically, speech energy, over a given period of time, will include a word, a pause, a word, a pause, and so forth. Additionally, stationary and dynamic noises may be present in the audio environment. As such, it can be difficult to accurately estimate the SNR. The SNR averages all of these stationary and non-stationary speech and noise components. There is no consideration in the determination of the SNR of the characteristics of the noise signal—only the overall level of noise. In addition, the value of SNR can vary based on the mechanisms used to estimate the speech and noise, such as whether it based on local or global estimates, and whether it is instantaneous or for a given period of time.
To overcome the shortcomings of the prior art, there is a need for an improved noise suppression system for processing audio signals.